The present invention relates to electric energy meters, and more particularly to the use of an isolated high voltage transformer within such a meter.
The use of electronics in electric energy meters has enabled the design of energy meters with greatly increased capability and functions. However, there is increasing pressure for such meters to have fewer parts and to be substantially smaller than previous designs. Fewer parts are required in order to minimize manufacturing costs including the cost of materials and assembly, and the subsequent cost and number of components which must be maintained for spare parts and repair purposes, along with an increase in reliability which accompanies designs which have fewer parts.
It is common to mount the power supply transformer for electronic registers in energy meters on a separate printed wiring board or plate positioned between the base of the meter and the register assembly. The present invention includes the mounting of the power supply transformer on the register printed circuit board in order to avoid the expense and space required through use of a separate printed circuit board or plate for the power supply transformer which requires additional mounting and interconnection. However, the use of a separate printed circuit board or plate positioned intermediate the base of the energy meter and the register printed circuit board is advantageous in that it isolates the primary side of the power supply transformer from the register printed circuit board. The low voltage circuitry of the register circuit board must be isolated from high voltage surges present on the power lines being measured and which are provided to the primary side of the power supply transformer since such surges may be in the order of up to 8,000 volts. In addition to isolating the register electronics from possible high voltages, it is desirable to avoid including the high voltage primary power circuit in the circuitry of the register printed circuit board.